At the present time foams and urethane plastics are made by reacting a polyol with an isocyanate with a functionality of at least 2 (two) or greater. The polyol can be a polyester molecule which has at least a functionality of at least 2 (two) or greater. The polyol can also be a polyether polyol which is made by reacting propylene oxide or ethylene oxide with a molecule such as ethylene glycol or glycerine to produce molecules with various molecule weights, which have pendant hydroxyl groups which will react with difunctional or multifunctional isocyanates to produce a solid plastic or foam. However at present time in order to produce a rigid foam or a urethane plastic it is necessary to react one part polyol with one part isocyanate. This is because the isocyanate generally contains aromatic rings and this is what makes the foam rigid, as well as having a high crosslink density.
Also, a major disadvantage of these high levels of isocyanate is that when the foam is burned, high levels of toxic gases are produced which are generally derived from the isocyanate part of the molecule. It would be a tremendous advantage to be able to reduce the toxic fumes.
It has been discovered that by using the lignin molecule as part of the polyol portion the significant advantages result. One is that by using the lignin molecule in the polyol portion of the system the amount of isocyanate can be reduced 40% or more and still produce rigid foam, This reduces the amount of toxic gases that are derived from the isocyanate portion of the system.
The lignin molecule is a natural phenolic type molecule that occurs in wood, straw, sugar cane and other natural materials. Generally the majority of the lignin that is produced as a byproduct of the pulping process to make paper is just burned to recover heat value. In the United States alone over 50 billion pounds lignin are burned annually just for its heat value. Any lignin from the Kraft pulping process, sulfite pulping process, semi mechanical pulping process, thermomechanical pulping process, semi-chemical pulping process, solvent process, steam explosion pulping process and biomass pulping process can be used.
As part of this present invention it was discovered that certain lignins can function quite well as a polyol component for an isocyanate system, these lignins can be used at different levels in the system depending on what final properties of the system are desired.
The use of the lignin molecule also significantly improves the moisture resistance of a foam, in fact when the proper level of lignin is used in a urethane foam the urethane foam will be almost impervious to moisture even when in direct contact with moisture. Commercial foams made with the present polyols literally absorb moisture like a sponge. Another major advantage of using lignin as a part of the polyol system is the flame resistance of the finished foam or urethane foam of urethane plastic part. This is because lignin acts as a natural flame retardant. However one of the major aspects of this invention is that the lignin molecule becomes readily soluble in polyether polyol that is made from ethylene oxide.
This is very important because when a regular polyether polyol is made from just propylene oxide the resulting polyol does not readily solubilize the lignin molecule and in many cases phase separation results and does not produce a quality urethane foam or plastic product. We have found that ethylene oxide as a part of the polyol makes it possible to make these blends with lignin.
What has been discovered is that where current polyether polyols only have marginal solubility for various lignins this fact makes it very difficult to produce a high quality foam or urethane plastic part because the lignin will tend to phase separate when the isocyanate is added to the lignin polyol blend and this makes it very difficult to make consistent physical products.
Also one of the major aspects of this invention is that in order to make high quality urethane foams and plastic materials the amount of sodium or other caustic ions such as potassium that are present in the lignin can have a dramatic affect on the properties of the final urethane product. This is because it is a well known fact that materials that produce a basic PH in water can perform as very strong catalysts for the isocyanate hydroxyl reaction that produces the urethane linkage. Therefore if the sodium level is too high it will cause the reaction between the hydroxyl groups and isocyanates go too fast which can produce a very poor quality product. It was discovered and it is one of the major aspects of this invention to reduce the sodium level to levels that are low enough to make it possible to produce a useful product once the lignin based polyol has reacted with the isocyanate. Also high levels of sodium ions or other inorganic ions such as potassium will actually degrade the foam in time.